In recent years, demand for performing high-speed data communication by wireless has been increasing. In particular, in a mobile environment and a wireless LAN (Local Area Network) environment, a diversity scheme and adaptive equalization processing have become indispensable, because multi-path (multiplexed radio wave propagation) fading occurs there.
Patent Literature 1 discloses an automatic equalizer which performs adaptive equalization processing by the use of an adaptive matched filter (AMF) and a decision feedback equalizer (DFE). The adaptive matched filter symmetrizes the impulse response of a transmission line, by estimating it from a received signal and realizing the inverse characteristic of the estimated impulse response. The decision feedback equalizer estimates inter-symbol interference in the transmission line on the basis of a received signal, and removes waveform distortion due to the inter-symbol interference.
In the automatic equalizer disclosed in Patent Literature 1, the adaptive matched filter and the decision feedback equalizer are connected in cascade. Then, the adaptive matched filter estimates the impulse response of the transmission line on the basis of a received signal. Further, the adaptive matched filter is connected in cascade with the transmission line, as a filter which realizes the inverse characteristic of the estimated impulse response. Thereby, matched signal, from which waveform distortion due to the impulse response of the transmission line is removed, is outputted. Subsequently, from the matched signal, the decision feedback equalizer removes waveform distortion due to inter-symbol interference. The decision feedback equalizer estimates the inter-symbol interference in the transmission line from the matched signal. Then, the decision feedback equalizer removes the inter-symbol interference by removing the temporally advanced interference component by the use of a forward equalizer inside the decision feedback equalizer, and by removing the temporally delayed interference component by the use of a backward equalizer also installed in the inside.
Patent Literature 2 discloses a technology of a diversity type receiver which performs adaptive equalization processing by the use of an adaptive matched filter and a decision feedback equalizer.
The technology disclosed in Patent Literature 2 is one which performs tap coefficient setting at initial start-up, by generating a known preamble signal included in a received signal also at the reception side, and by then using the generated preamble as a preamble for tap coefficient setting for the adaptive matched filter and that for the decision feedback equalizer. In the technology disclosed in Patent Literature 2, a preamble signal having a known waveform included in a received signal and a preamble signal generated at the reception side are used, and thereby, improvement in the stability of convergence of the adaptive equalization processing and reduction in a time to the convergence are conducted. That is, the technology of Patent Literature 2 makes tap coefficients of the adaptive matched filter and those of the decision feedback equalizer converge immediately, on the basis of correlation between the known preamble signal and the preamble signal generated at the reception side. Accordingly, the technology disclosed in Patent Literature 2 secures stability of convergence of the adaptive equalization processing and reduces a time required for the convergence.